Food Science Factoids!
Ways of preserving food:
Folks often ask me, "what is food science?" I've met young people at the farmers market with an interest in studying food science! Well, how about I provide some food science 101, methods of food preservation? Here’s a list off the top of my head of ways to extend the shelf life of food! Maybe you’ll find it interesting!
“Shelf life extension”: meaning slowing microbial spoilage,
and some slowing oxidation (“rancidity”) of pleasant flavors, unsaturated fats, and loss of pleasant textures (eg staling of bread, aka “moisture migration” which relates to water acivity (#2 below), however texture is really a whole other topic!)
Method 1. pH control (acidify or alkalize)
pH below 4.6 prevents botulism (plus having oxygen keeps away Clostridium botulinum which is anaerobic, although oxygen feeds other microbes, in particular molds; you can really spend a lifetime categorizing all the microorganisms, but basically there are anaerobic, aerobic, and "facultative anaerboes" meaning they can get by on no-oxygen but do better with oxygen. Evolution is an amazing thang!) Acidic or alkaline food environments: eg olives are typically alkaline brines; fermentation is a natural preservation process (if controlled) typically producing acetic acid or lactic acid, as well as alcohol! Alcohol is food preservative (since alcohol doesn't affect pH, significantly.) There are so many natural edible acids: citric, malic (apples), phosphoric (in cola, but today is not so "natural" and should arguable be avoided), tartaric (grapes and wine), acetic (vinegar, sour-dough bread), and lactic (yogurt and cheese.)
2. Water Activity: Big topic: sugar binds water; glycerin is a “humectant” (binds water); salt lower water activity; Dehydration! (My favorite process) lower water activity. Water activity ranges from 0 (absolutely no water available for microbes) to 1.0 (all water available for microbes.) Water Activity is the ratio of the food's "vapor pressure of water" (the evaporative pressure) is the numerator, the denominator is pure water. If water in the food can evaporate, the reasoning is that evaporating water in the food can also be used by microbes to multiply. An example of a food-liquid loaded with fermentable sugar but with a low water activity: HONEY!
3. Salt... Not only lowers water activity, but also causes microorganisms to swell and pop!
4. Heat sterilization (eg pasteurization of milk, “canning”, or “asceptic processing”)
5. Antimicrobial/antifungal perservatives/additives (eg sorbates and benzoates). Interestingly, these are also often pH acidifying, but these additives can enter cell membranes of microbes, whereas natural food acids like citric acid and lactic acid cannot because they are so water soluble, whereas sorbic acid and benzoic acid are more lipophilic/fat soluble.I do not like these chemical preservatives because benzoic acid can have trace benzene (a human toxin and both can cause headaches / histamine reactions in people.)
6. MAP: Modified Atmospheric Packaging (eg reduced/no oxygen and/or replace oxygen with nitrogen such as during wine bottling) or vacuum packaging (helps to a degree especially for flavor preservation.) A very effective approach especially for preserving fruits, such as inhibition of ethylene ripening gas. A chemical called "1-MCP" (1-Methycyclopropene) is used with Apples, Pears, Bananas, Avocados, Kiwis, Mangoes, Papayas, Tomatoes, Plums and Peaches! MCP is not permitted with organic fruits, but lower O2 is permitted.
O2 is lowered down to 1-2% (from about 21%)
CO2 is increased to 1-3%
1-MCP at for 12-24hrs (at 0.00005% to 0.0001%)
1-MCP then binds and inactivates a receptor that normally triggers release of ethylene gas which triggers ripening. Eventually, the fruit with deactivated receptors from MCP creates new receptors that are able to bind to ethylene, and a positive feedback loop is created causing rapid fruit ripening, almost like a chain reaction.
The MCP gradually unbinds or degrades over time and volatilizes. Because the human body does not have any receptors for ethylene, according to research from NC State, MCP has no effect on the human body.
7. Alcohol is a preservative! (but not really good for your liver.) You could say alcohol fits into category #5 above, but you could say the same about salt. Alcohol may even lower water activity a bit.
Preservatives have varying "mechanisms of action" on microbes that make all preservatives quite unique.
8. Smoke (very slight extension of shelf life but may also be carcinogenic.) Phenols released during smoking are anti-microbial. Acetic acid and other organic acids released during burning of wood can lower the surface pH of the food; Aldehydes such as formaldehyde and otehr reactive carbon compounds can cross-link proteins and surface sterilize food; Smoking was traditionally often done accompanying dehydration. The depth of penetration of the smoke is more on the surface 1-2mm and rarely exceeds 3-8mm depth. Smoking was often first salted, and then smoked. Smoking forms a sticky/tacky layer called a "pellicle."
A little bit of smoking however goes a long way towards adding a lot of flavor!
9. Antioxidants (for preserving flavors and unsaturated fats) eg vitamin E / tocopherols. Would you like some black garlic antioxidants with your olive oil? :-)
10. COMBINATIONS OF THE ABOVE!
I might have left some methods out... If you have any questions, see me during “TA office hours” at the market! (Disclaimer, I am no professor and was NOT the best student… by far!)
